Which is better, 5W40 or 10W40 engine oil?

[MacFernando]

5W40 engine oil is slightly better than 10W40, as it has stronger cold resistance and can be used in lower temperature conditions. The differences between 5W40 and 10W40 engine oil: 5W40 oil can withstand external low temperatures of -30°C, while 10W40 oil can withstand external low temperatures of -25°C. Both 5W40 and 10W40 can withstand external high temperatures of 40°C. 5W40 is more suitable for cold northern regions compared to 10W40. The "W" in 5W40 and 10W40 stands for winter, and the smaller the number before the "W," the lower the low-temperature viscosity, the better the low-temperature fluidity, the lower the applicable minimum temperature, and the better the engine protection during cold starts. In other words, 5W40 has a lower applicable minimum temperature than 10W40. The number 40 represents the high-temperature viscosity grade of the oil—the larger the number, the stronger the high-temperature viscosity, the thicker the oil film, and the better the sealing and protective capabilities.